1. Technical Field
This invention relates generally to integrated signal conditioning circuitry and, more particularly, to a temperature dependent voltage generator circuit and method for generating a voltage which is linearly related to changes in the operating temperature of the voltage generator circuit and which may be "nulled" or forced to equal zero in order to compensate for effects due to temperature variations.
2. Discussion
Integrated amplifier circuits are commonly employed for amplifying output signals produced by a transducer. The transducer and integrated amplifier circuit is generally calibrated during a calibration process to set initial gain and offset and generate a compensated calibrated output voltage. Often, these types of integrated circuits and transducers are subject to operating temperature variations which affect their operational characteristics. For example, operating temperature variations may affect the output of a transducer and, in turn, affect the gain and offset adjustments of an integrated amplifier circuit, resulting in an uncompensated output signal which may result in an inaccurate reading.
Typically, the gain and offset adjustments of an integrated amplifier circuit are adjusted at a first operating temperature such that the amplifier circuit generates a desired output signal. However, with variations in the operating temperature of the transducer and/or the amplifier circuit, unwanted effects on the output signal may be generated. Commonly, these unwanted effects are minimized by physically calibrating the individual components of the amplifier circuit prior to its final assembly. For example, the components may be individually calibrated with laser trimming techniques or through adjustment of resistive values of resistor networks by blowing fusible links. Unfortunately, these calibration techniques require physical access to the components of the amplifier circuit which are normally enclosed or encapsulated in a packaged housing after final assembly. Therefore, with laser trimming or fusible techniques, the calibration process must be performed prior to final assembly of the amplifier circuit.
Thus, it would be desirable to provide an integrated amplifier circuit and a method for compensating for signal variations due to changes in the operating temperature of the integrated amplifier circuit and/or a transducer without requiring physical access to the components of the amplifier. Furthermore, it would be desirable to provide a temperature dependent voltage generator circuit which generates an output signal which may be "nulled" or forced to zero at a first operating temperature and which thereafter generates an output signal that is proportional to changes in the operating temperature from the first temperature. For example, this output signal may be supplied to primary and secondary gain and offset circuits of an integrated amplifier circuit in order to compensate for the unwanted effects due to temperature variation.
One of the objects of the present invention is to provide a temperature dependent voltage generator circuit and method that generates an output voltage that may advantageously be "nulled" at any temperature and which thereafter, generates an output voltage that varies proportionally to changes in temperature.
Another object of the present invention is to provide a temperature dependent voltage generator circuit and method that employs a binary weighted current which is weighted by selectively coupling a plurality of current sources to the generator circuit so as to "null" the output voltage.